The present invention generally relates to a method and apparatus for evaluating a degree of a safety in traveling of a vehicle.
It is important for a driver to know the traveling condition of a motor vehicle that he is driving. It is particularly important for the driver to know a degree of a safety in traveling (i.e., traveling safety) of the motor vehicle. In this description, “traveling safety” is used to represent a degree of driving easiness and/or driving safety of a vehicle. A degree of traveling safety of a vehicle corresponds to a degree of slipping between a tire of the vehicle and a road surface on which the vehicle is traveling. In general, the larger the degree of slipping between the tire of the vehicle and the road surface, the lower the degree of driving easiness and/or driving safety of the vehicle in driving, and the higher the difficulty in driving the vehicle. Therefore, the larger the degree of slipping between the tire of the vehicle and the road surface, the lower the traveling safety of the vehicle. Conventionally, as an attempt for enabling a driver to know the degree of traveling safety of a vehicle that the driver is driving, various methods and apparatuses have been proposed.
For example, if a certain amount of cornering force and lateral force is applied to a vehicle during traveling, slipping occurs in a contact region between a tire and a road surface. If the degree of slipping increases to a relatively high level, driving (controlling) of the vehicle to which the tire is mounted becomes difficult. Therefore, the degree of slipping significantly relates to the traveling safety of the vehicle. JP 5-332889 A discloses an apparatus that measures a tire squeal sound by a microphone provided in the vicinity of a tire of a vehicle, estimates the contact condition of the tire against the road surface, based on the measured squeal sound, and generates an alarm to the driver according to the estimated contact condition. In this description, “squeal sound” means a sound having a frequency in the range of about 500 Hz to 1500 Hz, generated from a tire vibrating due to slippage between the tire and the road surface, as described in JP 5-332889 A. The squeal sound is generated due to tire vibration which occurs depending on the condition of contact between the tire and the road surface.
JP 2002-340863 A and JP 2003-182476 A, each propose a method and apparatus for evaluating the traveling condition of a tire based on the tire vibration that occurs depending on the contact condition of the tire and the road surface. JP 2002-340863 A discloses, as described in Paragraph 0014 of JP 2002-340863 A, a method and apparatus for determining a road surface condition, uses, as a reference, a frequency spectrum of acceleration data and a frequency spectrum of sound pressure that are obtained inside a tire when the vehicle is traveling at a constant speed on a dry road, so that a road condition is determined by detecting deviation from the reference frequency spectrum in a specific frequency during traveling. JP 2002-340863 A uses a frequency spectrum of an acceleration signal generated on a tire in the fore-and-aft direction of the vehicle to evaluate a road surface condition. JP 2003-182476 A discloses an apparatus for estimating a road surface condition and tire traveling condition aiming for improving the traveling safety of a vehicle. In the method proposed in JP 2003-182476 A, as described in Paragraph 0004 of JP 2003-182476 A, the condition of the road surface with which the tire is made in contact is accurately estimated under a constant traveling condition without any special action such as braking or steering. As described in Paragraph 0005 of JP 2003-182476 A, the method described in JP 2003-182476 A has been invented by noting the fact that the vibration level in a frequency spectrum of vibrations obtained by subjecting the vibrations in the circumferential direction or in the width direction of the tire during traveling to frequency analysis characteristically changes depending on the condition of a road surface with which the tire is made in contact, or the fault status of the tire. The invention described in JP 2003-182476 A, acquires information of vibrations of a wheel or suspension as the information that represent vibrations of the tire. The acquired vibrations are subjected to frequency analysis to obtain a frequency spectrum. Based on the vibration level in a specific frequency range of the obtained frequency spectrum, the road surface condition during traveling (mainly, coefficient of friction between road surface and tire) and the traveling condition (e.g., inflation pressure, wearing status, fault status) of the tire are estimated.